Reception of varying frequency signals



Sept. 13, 1932. E. s. PURINGTON RECEPTION OF VARYING FREQUENCY SIGNALSl Filed May 18, 1929 sub nwENToR E.S. PURINGTON HQBMBL IMHHHHRHY ATTORNEY Patented Sept. 13, 1932 wUnireoA STATES "PATENT,ePrice-1 l vnLLIsoN fs. PURINGTON, or GLOUCESTER, MASSACHUSETTS, ASSIGNOR 'ro JOHN HAYs HAMMOND, JR.

RECEPTION or VARYINGFREQENOY sIGN'ALs Aiipncation fried May 1e, i929.VA serial No. :se/1,221.

This invention relates toa method of receiving signals from continuous wave transmitters which are'so unsteady in the frequency radiated that they cannot be readily received by the usual methods. For example, a transmitter may vary as much as 1 KC in frequency during'the course of transmission Of a message due tomiscellaneous causes, such as swinging antennas and varying power supplies.

l It is an object ofthis invention to Vpermit reception of such unsteady or wobbled transmissions. r i v Itis an yObject Vof vthis invention to make it possible to receive continuous lfrequency signal's with constant pitch in the indicating phones in spite of variationsin the frequency transmitted.

A still further obj ect of this invention is to provide a new and improved system for. uninterrupted radio transmission.

A further object ofthis invention is to produce a pure-tone from a signalling radiation purposely scattered amongst several frequency channels at successive times, for yproducing secrecy of transmission.

A further object is to produce a reception means from a signalling-radiation purposely scattered among several frequency channels at successive times in order to minimize yselective fading. i

These .and other objects will become apparent from the following description taken in connection with the accompanying drawing.

This system accomplishes the above objects by using two local oscillators at the receiver of approximately the same frequency as the incoming radiations; y This may be considered to constitute the double superheterodyne. In carrying out the system of this invention three or moredetectors are provided, the usual first detector of the superheterodyne circuit, and two intermediate detectors. Y

The figure represents a receiving circuit embodying my invention". In this figure the antenna circuit 1 comprises an antenna, an input inductance, and the ground connection, and is adaptedV to receive the incoming frequency which I have designated as YW. 'In' ductively related to the inductance of the an'-v tenna circuit is a broadly tuned oscillatory circuit 2 connected to the grid'and filament of the 'detector 3 in the usual and well known manner through the grid 'leak 4 and the grid leak condenser 5. Also inductively related 'to the inductance of the oscillatory circuit 2 are the outputs of the local oscillatory circuits 6 and 7 which are adapted to producethe two heterodyning frequencies which are desig# nated'as Mand N. The detector tube 3 has inclndedin its output circuit arclosed oscillatory circuit 8 the inductance of which is inductively related-to theinput inductance 9 Ofthe filter amplifier 10 which is of the usual band pass type and adapted to transmitffre quencies of lVl-l/V and JV- N This filter amplifier 1 0 also includes as many intermediatefrequency amplifier stages as maybe desirable to properly amplify the selected frequencies, and is similar to the intermediate frequency amplifier of the usual sup'erhetero'- dyner circuit, except for the fact that it is rathermore broadly tuned in order to practically equally amplify throughout a slightly varying range of frequencies. y

In place of detector A55, l may substitute a pair of detectors, one of which receives part of the'incoming energy and also energy from M, producing MeYV, the other which receives part of the incoming energyV and also energy from N, producing tlf-N, said outputs of the two detectors being subsequently combined in amplifying filter 10. In this manner the input to 10 may be substantially free'frorn the difference frequency M-N oc# curring whenY one detector only is used.

- The output 11of the filter amplifier 10is connected to the input inductanceflQ of the detector 13, included in the input circuitof which is the grid'leak 14 and the gridllealx condenser 15. They output of this second detector l13 includes an inductance 16 inductively related to the yin'ductance 17 constituting the input ofthe filter 18. This filter 18 is adapted to pass frequency M4N and'eX- cludes all other frequencies. 'v Theoutput 19 of the filter 18 is inductively i related to the input inductance 20 of the third CII Also inductively related to the inductance 20 of the detector 21 is the output inductance of the local oscillator 24 which is adapted to produce a frequency The output of the third detector 21 includes an audio frequency device25 and a high frequency bypass condenser 26.

Each of the detector circuits is provided with the usual filament and plate sources as show-n. v

Having thus described my invention, I will now describe its operation. As above noted, I descrieed the incoming si frcqrfiency as W. This incoming signal is a continuous wave keyed to produce the signal but unsteady as to frequency. The two auxiliary frequencies M and N produced by the local oscillator are Vso arranged as to be constant and are adjustable so that the difference M-N may be kept constant preferably, for example, with M greater than the received signal W and N less than the received vsignal 7 by a substantially different amount. For instance, as follows:M-IV=0.4 (M-N) and IWL-N: 0.6 (M-N).

Then the three waves M, N, and W are impressed upon the first detector 3 of the figures, there will be produced bythe process of detcction.y among other current the fr-cquereies M-N, M-VV, and WV,- T, o which the nrst, M-N, is a constant frequency, constant amplitude current. The two remaining currents M-ViVT and VV-N exist only when there is an f v Jr.. s, a. incoming signal, and tary in infuienc. as

result of the unsteadiness or wobble of the incoming wave W. These three currents are impressed on the first amplifying filter 10 which comprises, as described above, amplifiers and other equipmentso arranged as to selectively amplify the currents of frequencies in the range of M-VV and VV-N, but reject currents of the frequency M-N, the remaining currents of frequencies M-V and VV-N existing as stated abovev only when there is an incomingsignal impressed upon the second detector 13.

It is well known in the mathematical treatment of detector actions that when voltages of Vtwo frequencies are impressed upon a detecting device, or any electrical device possessing a nonlinear'characteristic, with respect to the relation between input and output, there will be produced a. current of frequencies equal to the sum of the impressed frequencies, a current of a frequency equal to the difference of the impressed frequencies, and also the rst harmonics or overtones of the irnpressed frequencies. In the usual process of detection, the difference frequency is that utilized, but in the present invention, with W intermediate between N and M, I utilize the sum frequency and theother frequencies are rejected by means of the filter 18, Thus, the sum frequency due to the Adetecting of M--W and W-N, which is M-N, is the only frequency retained and is a current of constant frequency regardless of frequency variations in W. Furthermore, as no input will exist on the detector 13 in the absence of VJ, there will be no current in the output of filter 18 when there is no signal being received.

The current passed by the filter 18 is then impressed on the input of the third detector which serves to combine this frequency with -the locally Vproduced frequency (M N)`:tA.

This third detector thus produces an audio current A which, as can be readily seen, is of constant pitch regardless of the frequency of the incoming signal. The various other frequencies resulting from the combination of the frequency (M-N) iA and the sum frequency M-N passed bythe filter 18 are elimina-ted in the audio circuit as A is the only audible frequency present.

In case M and N are both greater or both less than IV, the second filter 18 utilizers the difference frequency in the usual manner, but this arrangement is not the preferable arrangement, because of the need of broader radio tuning to admit the three wave frequencies. i

By a proper choice of W, M, and :N, and by having M-N sufhciently above audibility, there will be no overlapping of the undesired unsteady current with the desired current of frequency of M-N.V Such proper relationp ship exists, for instance, when M-.W==0.4 (M -N)` and WN) :0.6 (M-N) and when M-N is a ove audibility. Thus, with a carrier frequency of 1,000 KC and M-N=10KC M would be 1,004 KC and N 994 KC. This current of M-N impressed upon the second detector, it must be remembered, exists only when there is an incomingsignal, and any steady and unkeyed 'current ii:-

as described to beat with the frequency M-N in the input of the third detector, resulting in a tone of constant pitch A, being received 1n the indicating headphones whenever there 1s an incoming signal.

Having thus described my invention, it is to be understood that- I am not to be limited by the specific embodiments of my invention shown and described herein for the purpose in the appended claims.

0f illustration, but by its scope as set` forthA I claim: a l. Means for the reception of variable frequency signals which comprises an input -quencyffsignals which comprises, Ytwo local Y 4oscillatorsjfor producing frequencies Vdiffercircuit, a rst detector, an input circuit for said first detector, a local oscillator producing a high frequency differing from the received frequency, a second local oscillator for producing a low frequency dierino from the incoming frequency by an amount which is different than the difference of the first local oscillator therefrom, an output circuit for said first detector, a filter circuit inductively related to said output circuit, and adapted to filter from thev output of said first detector all frequencies except the difference frequency between the high heterodyning frequency and the received frequency, and the difference frequency between. the received frequency and the low heferodyning frequency, and to amplify the frequencies passed, a second detector associated with the output of said filter circuit for combining the two di fference frequencies existing in the output of said first filter, a second filter for removing from the output of said second detector all frequencies except the frequency produced by said last combining, corresponding to the difference of the two local oscillators, a third detector associated with the output of said last mentioned filter, a third heterodyning frequency source for producing a frequency which, when combined with said last produced frequency, will cause a constant audio frequency, and a utilization circuit for said audio frequency. i

2. Means for the reception of variable fre.- quency signals which comprises, a local oscillator for producing a highl frequency differing from the received frequency, a second local oscillator for producing a low frequency differing from the received frequency, differently than the first local oscillator, a first detector for combining the received frequency and the locally produced frequencies, a filter circuit adapted to filter from the output of said first detector all frequencies except the difference frequency between the high heterodyning frequency and the received frequency, and the difference frequency between the reoeived frequency and the low heterodyning frequency, and to amplify the frequencies passed, a second detector for combining the two difference frequencies passed by said first filter, a second filter for removing from the output of said second detector all frequencies except the sum frequency produced by said last combining, equal to the difference of the two local frequencies, a third heterodyning frequency source for producing a frequency which, when combined and detected with said last produced frequency, will cause a'constant audio frequency, a third detector for combining the said frequency and the last mentioned heterodyning frequency, and a utilization circuit `for the audio frequency 'pro'duce'd'rby said c.fuirbining` fr 3. Means forthe receptionof variable 'freing by ay different amount from a received frequency, a .single first;detector for` combining the received frequency and the locally produced frequencies, an amplifier and filter vcircuit adapted to filter from the output of .said rst detector all frequencies except the .dierencefrequencies between the ,two heterodyning frequencies and the received vfre- ;quency, .and to amplify the frequencies passed, a fsecond detector for combining'the twodifference frequencies passed by said first filter, a Ysecond filter for removing from the Voutput of said second detector, all frequenfdo ciesexcept the sum 'frequency produced by said last 'combining equal to the difference of the two heterodynlng frequencies, a third neterodyning requency source for'producing la frequency which, when combineill with said last producedfrequency, will cause a constant audio frequency, `and a third detector last for a producing said constant audio frequency.

Il. Means for thereception of variable fre- Y quency signals whichv comprises, means for producing three heterodyning frequencies, means for combining the received frequency with two of the heterodyning frequencies,

means for filtering from the output of saidv combining means all frequencies except the dierence frequencies between the heterodyning frequencies and the, yreceived frequency produced by said combining means, a second combining means associated with the filtering means for combining the two resulting diderence frequencies, a second filtering means for removing from the output of said' second combining means all frequencies except the sum frequency produced by said last combining equal to the difference of the first two heterodyning frequencies, and a third combining means associated with the output of said last mentioned filtering means for combining the third heterodyning frequency with the last mentioned dierence frequency and thus producing an audio frequency.

' 5. Means for the reception of variable frequency signals which comprises, means for producing three heterodyning frequencies,v

means for combining the received frequency with two of the 'heterodyning frequencies, means for filtering from the output of said combining means all frequencies except the difference frequencies between the heterodyning frequencies and the received frequency produced by said combining means, a second combining means associated with the filtering means for combining the two resulting difference frequencies, a second filtering means for removing from the output of said second combining means all frequencies eX- cept the sum frequency produced by said last combining', equal to the dilference of the `first two heterodyning frequencies,a third combining means associated withlthe outputV of said lastmentioned ltering means for combining the third heterodyning' frequency with the frequency equal to' the differenceof the first two heterodyning frequencies, and thus producing an audio frequency,`and a utiliza tion circuit for said audio frequency. y

6. The method of reception of signal ener'gy Which comprises, combining the incom- -ing signal energy with locally generated oscillations having aV frequency Vhigher than the frequency of the incoming signal 'energy and with locally generated oscillations having a frequency lower than thefrequency of the incoming energy, each of said locallygenerated frequencies differing from the incoming frequencyby'a different amount, producing from said combination energy having a frequency equal to the frequency of the incoming `energy minusthe frequency of the second i named locally generated energy and also energy of a frequency equal to the frequency of the first named locally generated energy mi'- nus the frequency of Vthe incoming energy, combining the two resulting frequencies and producing therefrom energy having a frequency equal to the difference between the two locally generated frequencies, combining the last resulting energy with energy having a frequency differing therefrom by an. audible frequency and producingfromsaid last coinbination audible frequency energ y v v ELLISON S. PURINGTON. 

